The large coop is stationary and easy to secure with a padlock.
The problem with a chicken tractor (where the chicks are) is that it's PORTABLE. Even if I were to put an actual lock on the gate, what's to stop a human from picking up the whole thing? I'm barely 5ft and I built it so I can move it all around myself. It kept my other 6 chicks safe from 3 to 20 weeks - - - it's pretty secure from your normal predators, but humans are a whole nother ballgame.
I could put the chicks in with the adults at night (in a dog crate) to lock them all up, but then what would I do with them in the daytime while the adults range?
Have you looked for tracks in the dirt? That's where I look when I suspect suspicious activity around my coops. You can also rake the ground smooth before you leave for the night, even sprinkle flour all around the gate & pen, to help you see the tracks better in the morning.
And you say you had 4-week-old chicks missing before you trapped the neighbor's cat? Don't you think the cat could be the culprit? I don't know how you had your extension cord set up, but the cat could have also caused the light to become unplugged if he stepped on it or got a leg tangled in it.
I hope you solve your dilemma soon.
Our yard is pretty grassy, no tracks.
The neighborhood is full of cats, and they never got any of my chicks before even when Houdini used to escape pretty often (she's now a laying pullet, about 30 weeks old) - much less 3 in one day!
Cats generally play with their food, you know, evidence. I know if it was one of my cats, the body would have ended up on my back porch/steps
The extension cord is laying flat on the ground. It fits pretty snugly, I don't think a human stepping on it would unplug it, much less a little cat. I've run extension cords all over the yard, since I move the tractor a lot having permanent electricity wouldn't work very well and I've never had it randomly come unplugged before.
I did ask the neighbors if they had seen anything. The mom said no, the daughter said something but I'm not sure what. COULD be the kids that's my best guess.
Caught another cat in the trap while I was gone to work. I'm on the fence about what to do with it because I really wish our neighborhood had a TNR type program.